[FFmpeg-trac] #10732(undetermined:new): avcodec_flush_buffers() not resetting E-AC-3 decoder

[FFmpeg]

#10732: avcodec_flush_buffers() not resetting E-AC-3 decoder
----------------------------------------+----------------------------------
             Reporter:  Peter Krefting  |                     Type:  defect
               Status:  new             |                 Priority:  minor
            Component:  undetermined    |                  Version:  5.0.3
             Keywords:                  |               Blocked By:
             Blocking:                  |  Reproduced by developer:  0
Analyzed by developer:  0               |
----------------------------------------+----------------------------------
 Summary of the bug:
 I am reusing the same AVCodecContext to decode several parallel E-AC-3
 audio streams. As per documentation I am calling
 [https://ffmpeg.org/doxygen/trunk/group__lavc__misc.html#gaf60b0e076f822abcb2700eb601d352a6
 avcodec_flush_buffers()] between each decoding run. This seems to work for
 most codecs, but when used with the E-AC-3 decoder the output is not
 identical between runs

 How to reproduce:
 {{{#!c
 #include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
 #include <stdio.h>
 #include <assert.h>

 int main(int argc, char *argv[])
 {
     const AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_EAC3);
     AVCodecContext *decoder = avcodec_alloc_context3(codec);
     avcodec_open2(decoder, codec, NULL);
     assert(decoder->sample_fmt == AV_SAMPLE_FMT_FLTP);

     for (int l = 0; l < 2; ++ l)
     {
         printf("[%d] Reading file\n", l);
         avcodec_flush_buffers(decoder);
         AVFormatContext *avf_ctx = NULL;
         avformat_open_input(&avf_ctx,
 "file:i28553p303t610156395819694.ac3", NULL, NULL);
         avformat_find_stream_info(avf_ctx, NULL);

         AVPacket avpkt = { 0 };
         while (av_read_frame(avf_ctx, &avpkt) == 0)
         {
             avcodec_send_packet(decoder, &avpkt);
             AVFrame *frame = av_frame_alloc();
             avcodec_receive_frame(decoder, frame);
             printf("Got %d samples in %d channels\n", frame->nb_samples,
 frame->channels);

             for (int i = 0; i < frame->nb_samples; ++ i)
             {
                 printf("%4d:", i);
                 for (int j = 0; j < frame->channels; ++ j)
                 {
                     printf(" [%d]%f", j, ((float *) frame->data[j])[i]);
                 }
                 printf("\n");
             }

             av_frame_free(&frame);
         }
         avformat_close_input(&avf_ctx);
     }

     avcodec_free_context(&decoder);
     return 0;
 }
 }}}

 The test file is available here:
 https://e.pcloud.link/publink/show?code=XZS8y1ZlEryJIDYU0yIzDTUhw1sDfHDRtUV
 and contains a ten-second extract of an audio track from an MPEGTS
 container, captured off-air while looking at a problem where the encoder
 suddenly only outputs silence.

 I expect the output to be identical on the first and second run, but that
 is not what I am seeing:

 {{{
 $ ./decode |grep -A5 'Reading file'
 [eac3 @ 0x55fc4b0a5ec0] Estimating duration from bitrate, this may be
 inaccurate
 [0] Reading file
 Got 1536 samples in 6 channels
    0: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
    1: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
    2: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
    3: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
 [eac3 @ 0x55fc4b11a840] Estimating duration from bitrate, this may be
 inaccurate
 --
 [1] Reading file
 Got 1536 samples in 6 channels
    0: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
    1: [0]-0.000000 [1]0.000000 [2]-0.000000 [3]-0.000000 [4]-0.000000
 [5]-0.000000
    2: [0]0.000000 [1]0.000000 [2]0.000000 [3]0.000000 [4]0.000000
 [5]0.000000
    3: [0]-0.000000 [1]-0.000000 [2]-0.000000 [3]-0.000000 [4]-0.000000
 [5]-0.000000
 }}}

 In real life we are also interleaving other E-AC-3 audio streams from the
 same MPEGTS between decodes, and see that the initial decoded samples
 differ even more than when just redecoding the same sample over and over.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10732>
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